Photolithography is a process to fabricate an integrated circuit after the integrated circuit is designed. In the photolithographic process, a photomask, or more simply a mask, is used to lithograph a mask pattern, which is similar to the physical layout of a layer of an integrated circuit, onto a wafer surface. With the continuing scaling of feature size of chips, the pattern size on a photomask is also reduced. As a result, the non-linear imaging effect happens, i.e. the resolution of a photoresist pattern begins to blur, when the pattern size goes beyond the resolution limit of the photolithographic process. Conventionally, a technology of double patterning is developed for photolithography to enhance the feature density. The double patterning is enhanced to produce twice the expected number of features.
Like reference symbols in the various drawings indicate like elements.